The present invention relates in general to sewing machines and in particular to a new and useful sewing machine equipped with a device for producing corner seams.
Such devices include a sensor which is located ahead of the needle in the stitching direction, which sensor is operable to release mechanisms for stopping the needle at a predetermined corner point of a work or workpiece, as soon as an edge of the work or workpiece passes the sensor.
In a prior art arrangement of this kind (U.S. Pat. No. 4,226,198), a sensor releases certain operations for stopping the needle during the production of the last stitch to be made. Upon finishing the last stitch, the feed is stopped. The last perforation made when the needle has stopped is therefore mostly off a desired exact distance from the work edge which was sensed and which caused the stop. This distance can be anywhere within a zone spanning the complete stitch length, since the stitch which was already started must be finished.
For this reason, the sensor of the prior art, was usually placed so as to release the mentioned operation already in advance of the corner position, wherefore the last perforation by the needle is made somewhere in the area within a half stitch length before and behind the exact corner position. Such a stitch results in an unfavorable aspect of the corner seam and will frequently be rejected. Since the sewing machine, normally running at a high speed, cannot be stopped instantly, another sensor must be provided in addition, upstream of the first one, to reduce the speed of the machine some stitches before the stopping of the needle. Only then can the stopping operation depending on a response of the first sensor, follow.